MindTheGap
325 posts
Mar 08, 2014
12:00 AM
|
People here often talk about a particular amp/mic being prone to feedback, or being resistant to feedback. I have limited experience but have noticed these things:
- my 5W amp is much more likely to feedback at a given volume than pretty much any setup using the Harp Break pedal (including into the same amp), with a similar amount of gain/crunch.
- There seems to be a mysterious 'field of feedback' as you move the mic around the amp, not necessarily where you might expect it to be.
- The cupped mic picks up less ambient sound, and it is muffled, yet is more prone to feedback.
Is it just a case of try-it-and-see with each configuration, or are there useful rules of thumb?
----------
MTG
|
SuperBee
1736 posts
Mar 08, 2014
2:37 AM
|
I find that very interesting. When I had a harp break I found any rig was prone to feedback at a lower volume when using the pedal than when not using it. As I really needed to be loud as possible at the time, I found the pedal very frustrating and sold it .
Gain is a killer. For me, rule of thumb is keep gain low.
|
MindTheGap
329 posts
Mar 08, 2014
3:03 AM
|
I agree, it's counter-intuitive. And since you've had the opposite experience, maybe dependent on the other factors like the type of amp or mic.
I read many times about keeping gain low, and I understand exactly why that's an issue. And the HB is potentially adding gain. So it must be something around the rounding/clipping it does, or possibly changing the EQ? Both things change the spectrum of frequencies in the signal.
Could be a perception thing e.g. the bass boost from the HB makes it sound louder than it is. Like the 'Loudness' button on old Hi-Fi amps, which didn't change the volume so much as changed the eq to that of a loud sound, far away.
The stock explanation I have read of why tube guitar amps sound louder than solid state ones is around perception: you can turn them both up the same, but when the power section of the tube amp is distorting you celebrate the warm crunchy sound, and when the solid-state amp is doing the same thing it sets your teeth on edge and say how horrible transistors are. Feel free to correct me, this is just what I've read.
It all seems a bit Bermuda Triangle, which is why I ask.
----------
MTG
Last Edited by MindTheGap on Mar 08, 2014 3:13 AM
|
MN
312 posts
Mar 08, 2014
4:10 AM
|
Main rules of thumb for me: If feedback's a problem with a bullet, try an SM 57. Also, learn to tongue block and overblow. I'm not saying that these two techniques cause less feedback. But in learning them, your playing will become more resonant and full bodied because you have to learn to play from deeper down on the gut. As a result, you get more volume through the mic and don't have to crank the amp's volume so high. Whether or not you use TBing or overblows in your preferred style of music, getting comfortable with each WILL improve your tone.
|
Goldbrick
330 posts
Mar 08, 2014
5:44 AM
|
As to the last part about tube vs, solid state sound
simply put a good tube amp is driven into distortion at a more gradual rate -distortion harmonics from tubes are generally more pleasant to the ear. Solid state clips more harshly and so unless their is some emulation built in or via pedal it just doesnt sound as musical
Also since ratings are based on clean sound - a tube ampcan be pushed harder without sounding like crap so it generally can have more useable power at its limits-compared to an equally rated ss amp. Watts are Watts-its just how those watts are used ( sorry Charlie)
There are lots of scientific explanations but that is the quick and dirty
Last Edited by Goldbrick on Mar 08, 2014 7:42 AM
|
Barley Nectar
312 posts
Mar 08, 2014
7:02 AM
|
-No Harp Break, no comment.
- When doing this feedback occurs at a specific frequency. The feedback is caused by ambient noise that the mic is receiving and the amp is amplifying. Think of this frequency as a wave form in space. As you move the mic around you are changing the point on the waveform that the mic is relative to. When this point is in phase with the output of the mic, feedback occurs. This is why small movements of the mic will change the properties of the feedback zone. It has to do with the wavelength of sound. Thats the way I see it, hope this makes sense.
-Not too sure about this one either. I think this depends on the mic used. I have experienced this also.
Rule of thumb: Do not stand in front of your amp like guitar guys do. Stand beside and slightly away. This will help reduce feedback. The old blues men often used house PA systems that were tube type. The speakers were remote from them,(up on the wall/stand/shelf), this reduced the direct interaction between the amp/speaker and the mic. Good luck...BN
|
Rick Davis
3041 posts
Mar 08, 2014
8:05 AM
|
Rules of thumb for feedback:
-In smaller enclosed spaces like your living room or garage you will more likely get feedback through your amp.
-In rooms with parallel reflective surfaces you will be more likely to hear feedback.
-Amps with high gain in their pre-amp stages will more likely produce feedback. This includes most modern guitar amps.
-Your technique plays a big part in the presence or absence of feedback in your playing.
-The standard remedies work: Replace pre-amp tubes with lower gain tubes, roll off the highs, use a less-bright speaker.
-A custom harp amp is already sorted and will feedback much less. The extra cost is mitigated by the ease of use and the savings on pedals and other mods that you will not need. (Full disclosure: I make and sell the Memphis Mini harp amp.)
-You should exhaust all of these rules of thumb before throwing money at any kind of anti-feedback pedal. They are expensive, they work in a narrow range of circumstances, and they all rob your tone in some way.
----------
-Little Rick Davis
The Memphis Mini harp amp
The Blues Harp Amps Blog
The Mile High Blues Society
|
MindTheGap
331 posts
Mar 08, 2014
9:09 AM
|
Thanks for the info. It's esp. useful to understand what you can do to improve things without changing equipment - i.e. what to do in-situ. I can understand the parallel walls thing, maybe angling the amp L-R or up/down might help. And with Barley Nectar's point about feedback zones and wavelength, maybe moving towards-away from a wall will have an effect.
I can believe that technique has an effect, but that does take time. Good to have my understanding of the 'tube amps are louder' effect verified by Goldbrick.
Re the Memphis Mini, I see you advertise it as '...very feedback resistant' Not looking to uncover your trade secrets, but does that come out as a by-product of making it sound good, or do you design specifically for that feature?
Plenty to try out from this, thanks.
----------
MTG
|
Rick Davis
3043 posts
Mar 08, 2014
9:51 AM
|
MTG, that is by design. As I wrote above,"Replace pre-amp tubes with lower gain tubes, roll off the highs, use a less-bright speaker." There are some elements of the design that are proprietary but that is the basic gist of it.
Using a line out to the PA instead of a mic'ing the amp is a good way to eliminate a very nasty feedback potential. But I think that is beyond the scope of your question.
As far as technique, the most important thing to work on with respect to feedback is your mic cupping. Pretty easy. Try to isolate the mic from the sound of the amp. You don't need to squeeze it in a death grip, just get a nice seal. Here is a video of Ronnie talking about this at one of his seminars. There are other good videos on this too.
----------
-Little Rick Davis
The Memphis Mini harp amp
The Blues Harp Amps Blog
The Mile High Blues Society
Last Edited by Rick Davis on Mar 08, 2014 9:52 AM
|
nacoran
7585 posts
Mar 08, 2014
11:46 AM
|
And the way you cup the mic!!! Your hands can act as little acoustic chambers. If you are playing 'acoustically', i.e. backed off from the mic, you will get less feedback, but of course, that won't always give you the tone you are looking for. Sometimes just adjusting the way you are cupping the mic can stop feedback. Volume control on a mic, or even just an emergency on off switch are nice too. :)
----------
Nate
Facebook
Thread Organizer (A list of all sorts of useful threads)
|
SuperBee
1737 posts
Mar 08, 2014
1:47 PM
|
I agree it's important where you stand. When things were loud, I'd stand to the side and just ahead of the amp, so I could hear well but the mic couldn't.
But also, if you are going to use an amp on stage make sure it's loud enough to serve as your monitor. If it's not loud enough and you need to get support from the PA in the monitors, things can get tricky.
For a long time I thought a 410 was overkill. No, it's great. The way to go. I'd rather not lug it but in all other ways it makes life easier.
Whenever I play with drums, now I use the 410. Just means I'm not always having to push for max volume, can employ dynamics in my playing...and feedback is a rare visitor.
Mics...I like the volume control. I'd rather use the blowsmeaway in line control than a built in. An on/off switch would be ok too, I usually have the volume up full.
|
jbone
1533 posts
Mar 08, 2014
1:55 PM
|
I have been on many a stage and had to deal with this. I have used a lot of amps and mics as well. My amps almost always get a 12au7 for the pre amp. I set my volume per situation but generally the highs are dropped down. I have to sit close to the amp a lot of times but if I point it slightly to the side this helps.
A volume pot or on-off switch also helps since many times feedback occurs with the mic "at rest" ie when you are not playing. This is when I cut mic volume back, and maybe just to a fill or comp until it's solo time. I've used a Lone wolf Harp Delay which has helped ease a lot of this as well.
I don't play loud gigs any more. This makes it easier to control volume and feedback. It also saves my voice.
I have several mics I use but my current favorite is a Shure 585 ball mic. I set it in a stand and don't move around on stage with it. When I use a bullet it's with a cm element usually and that will be prone to more squeal if care is not taken. Sometimes a crystal element mic like a jt30 or an Astatic 332 is what's called for and that's when I really drop any highs out. The response on a crystal has very light bass so bass gets turned up on the amp.
----------
http://www.reverbnation.com/jawboneandjolene
https://www.facebook.com/profile.php?id=100000386839482
http://www.youtube.com/watch?v=wa7La7yYYeE
|
slackwater
17 posts
Mar 08, 2014
3:49 PM
|
Of course, different setup's are going to respond differently, but I find that the key to the Harp Break(with regards to feedback) is the volume control- more drive, less volume. However you probably do that anyway, maybe it's an issue of your five watter's headroom?
I've got a Harp Octave too and found that it's great at sounding louder without increased feedback issues. It gives me a bit of grubby girth too. I don't know why but it just seems to work.
-jbone mentioned the thing of feedback 'at rest'. Well, I don't have one, but a noise gate sort of thing, can help there too, apparently the Lone Wolf Harp Shield does it alright. Or just use a volume control or an on/off of course- if there's no volume control on your mic but your using pedals well they've mostly got a volume control on them which will do the same thing.
|
Rick Davis
3045 posts
Mar 08, 2014
4:30 PM
|
Slackwater, I know you are not suggesting this, but if a new player bought all three of those pedals it would cost him $439 (more than the cost of many amps) and it would still not solve his feedback issues.
----------
-Little Rick Davis
The Memphis Mini harp amp
The Blues Harp Amps Blog
The Mile High Blues Society
|
slackwater
18 posts
Mar 08, 2014
8:58 PM
|
Yeah your right Rick ,on both counts. I'm not trying to sell him anything but he started talking about a pedal so I spoke to that. Much of the other rule of thumb stuff, as he called it, like gain, relative position of mic to amp, cupping and bigger amp/more speakers etc. had already been touched on by others
|
SuperBee
1741 posts
Mar 09, 2014
2:35 PM
|
Feedback and mic cupping:
I haven't had this problem much.
At a recent open mic I was asked to perform. I hadn't planned to but I had a harp in my pocket so I went up. When I cupped the vocal mic it squealed. I think it was a sm58...a mic I have used enough to know it wasn't simply the mic to blame. I assume the mic was set for vocals by folks who stand back a little...you know, guitar players and such, and the gain was just too high to cup. I don't actually understand the physics of what's happening here though.
RoT would be, do a sound check ? And keep gain only as high as necessary
|
MindTheGap
341 posts
Mar 10, 2014
5:56 AM
|
Rick, Slackwater - thanks, I want to understand all the angles, so all info is welcome. Rick, on your blog, I've read that using a lower-gain tube is equivalent to lowering the input volume e.g. with a mic pot or the volume on the HB pedal. Have I got that correct?
SuperBee - Yes that's the effect. You'd have thought that cupping the mic would up the signal from the harp, and lower the ambient signal and so reduce the feedback. I don't know the physics of it either, but I suspect resonance - that's normally the secret extra bit. As Nate refers to, hands acting as little resonating chambers.
----------
MTG
|
jpmcbride
34 posts
Mar 10, 2014
12:41 PM
|
MDG said "... or possibly changing the EQ? Both things change the spectrum of frequencies in the signal"
When I was new to harp I went to a Jam Camp and Jason Ricci gave a class on basic amp setup. He said something that I continue to tell every beginner when they ask me about setting up their amp (and I get a lot of these questions because I sell mics).
He explained how gain was the enemy. Then said "and tone knobs are just frequency selective gain".
----------
Jim McBride
www.bottleoblues.com
|
Greg Heumann
2641 posts
Mar 10, 2014
12:56 PM
|
When you cup a mic your hands can act like a satellite dish, actually directing MORE ambient sound to the mic - hence, feedback. Remember, the mic has to pick up sound coming from the amp to complete the feedback loop - so once you're are PLAYING in cupped position, feedback should be less of a problem.
When you HAVE to play at the hairy edge of feedback - you CAN control things - sometimes placing the mic against your chest when not playing can help - though because a 58 can pick up from the sides much more than a bullet this may not help. A volume control always works.
----------
***************************************************
/Greg
BlowsMeAway Productions
See my Customer Mics album on Facebook
BlueState - my band
Bluestate on iTunes
|
MindTheGap
344 posts
Mar 11, 2014
2:05 AM
|
Jim - Re tone controls, I can see that. I don't know how notchy a typical amp tone control is, but you could imagine it boosting a particular frequency and inducing feedback. On that note, maybe eliminating lumps and bumps in the amp's response spectrum is part of the magic of harp amp design.
Greg - yes that does seem to be the case. I did a bit of experimenting after reading this, and it did need a really tight cup (i.e. that thing you demo with the harp sealed against the cheek) to reduce the feedback when in that state. I can see why a volume control on the mic is so important.
Just to say, I'm not having a massive feedback problem, but it's clearly there as something that needs to be understood.
Wasn't the history of the development of the solid-body electric guitar about dealing with feedback? Look at the result of that! Imagine a world where there harp-feedback is eliminated - not entirely good - maybe it was put there for a reason :-)
----------
MTG
|
Greg Heumann
2642 posts
Mar 11, 2014
11:25 AM
|
Guitar strings/pickups aren't nearly as efficient at coupling to sound waves as a microphone. Also, the pickups' output is not as high as a mic. But yes, slid body guitars helped deal with feedback for guitars because the hollow body is a resonance chamber.
Feedback is a clear and natural phenomenon - ANY amplifier/mic combination will feedback at some point. Less sensitive mic? Less feedback. Less gain amp? More control.
----------
***************************************************
/Greg
BlowsMeAway Productions
See my Customer Mics album on Facebook
BlueState - my band
Bluestate on iTunes
|
